In recent automotive technology, attention is being given to in-wheel motor drives, each of which is partially or entirely mounted in an interior space of a road wheel to drive the wheel. A conventional in-wheel motor drive is disclosed in, for example, Japanese Unexamined Patent Application Publication No. 2008-44537 (PTL 1). The in-wheel motor drive in PTL 1 includes a drive motor, a speed reducer that receives a driving force from the drive motor, reduces the rotational speed and outputs it to a wheel, and a wheel hub member that is connected with an output shaft of the speed reducer, the drive motor, speed reducer and hub member being coaxially arranged in a line. This reducer adopts a cycloid reduction mechanism that provides a higher reduction ratio than that of conventional planetary gear speed reduction mechanisms known as general speed reducers. Thanks to the cycloid reduction mechanism, the torque required by the drive motor can be set smaller and the in-wheel motor drive can be reduced in size and weight.